House-broken animals, such as cats, are trained into the habit of urinating and defecating in a specially provided litter box. Similarly, untrained and caged animals, such as guinea pigs, urinate and defecate on the floor of their cage, often in approximately the same floor area of the cage. Consequently, pet owners, homeowners, veterinarians and laboratory personnel have added absorbent materials to the litter box or cage to collect the urine and feces. After a relatively short period of time, the dross-soiled absorbent emits objectionable odors because of the presence of the urine and fecal matter.
In order to reduce or eliminate these objectionable odors, homeowners periodically physically remove the fecal matter from the litter absorbent. However, physical removal of the feces does not reduce or eliminate odors caused by the urine absorbed into the absorbent. Therefore, when the odors caused by the absorbed urine become intolerable, the homeowner discards the litter box absorbent material entirely. The homeowner then washes the litter box and refills the litter box with fresh litter box absorbent material. These activities are unpleasant, time-consuming and expensive. Consequently, the litter box absorbent material usually is a relatively inexpensive solid absorbent material, such that an individual cleaning of the litter box is not particularly economically burdensome. However, repeated litter box cleanings over a period of time account for relatively large expenditures.
The most commonly used litter box absorbent materials are inexpensive clays, such as calcined clays, that are safe and non-irritating to the animals, and that absorb relatively substantial amounts of liquids. Other porous, solid litter box absorbent materials, that are used alone or in combination, include straw, sawdust, wood chips, wood shavings, porous polymeric beads, shredded paper, sand, bark, cloth, ground corn husks, cellulose, and water-insoluble inorganic salts, such as calcium sulfate. Each of these absorbent materials has the advantage of low cost, but each suffers from the disadvantage of merely absorbing a liquid waste product and holding the product within its porous matrices, or, in the case of sand, adsorbing the liquid dross on its surface. For each absorbent material, offensive odors are eventually caused by the absorbed urine, and the entire contents of the litter box, including soiled absorbent material and unsoiled absorbent material, has to be discarded.
An improved composition for animal litters are the clayey soils or comminuted rocks, e.g. the sodium bentonites, comprising at least one water-swellable clay mineral in the montmorillonite clay family. These materials have the ability to clump and harden after contact with an aqueous liquid such as urine. This facilitates the removal of only the soiled portion of the litter in a litter box or cage during cleaning without the necessity of removing all the litter.
With regard to the odor problem connected with the use of animal litters, various deodorizing agents have been recommended for use in such litters, including sodium bicarbonate (SBC). However, when SBC is utilized in the form of an unmodified powder as a deodorizing agent in animal litter and is exposed to the aqueous phase of any animal waste product, the aqueous phase tends to wick across the surface of the animal litter. Furthermore, due to its relatively high density, it tends to sink to the bottom of any litter composition present in the cage or litter box. To overcome these disadvantages, it has been proposed that the SBC be utilized in the animal litter in encapsulated form. However, the preparation of encapsulated SBC is an expensive procedure which renders the employment of SBC in this form impractical for many applications.
The following prior art references illustrate aspects of the technology of animal litter preparation, and, in particular, disclose the use of clays in such litters.
U.S. Pat. No. 3,765,371 issued Oct. 16, 1973 to Fisher, discloses a foamed plastic for absorbing and/or adsorbing animal waste products and also identifies clay and bentonites as previously used animal litters.
U.S. Pat. No. 4,275,684 issued Jun. 30, 1981 and U.S. Pat. No. 4,395,357 issued Jul. 26, 1983 to Kramer et al., disclose calcium silicate as an animal litter box absorbent material, and state that clay minerals, e.g. sepiolites, are known litters.
U.S. Pat. No. 4,315,761 issued Feb. 16, 1982 to Larrson et al., teaches the use of aerated or foamed concrete to absorb animal waste products and facilitate the removal of excrement from a litter box, and also discloses that “porous granulates of burnt expanded clay” are known for use as a urine absorbent.
U.S. Pat. No. 4,494,481 issued Jan. 22, 1985 to Rodriguez et al., discloses the addition of a soluble salt of a transition metal from Group Ib or IIb of the Periodic Table to a conventional litter composition to prevent the development of urine odors, and also identifies “clay such as . . . montmorillonites or bentonites” as suitable for use as an animal litter.
U.S. Pat. No. 4,570,573 issued Feb. 18, 1986 to Lohman, discloses an animal litter composition containing 60–94 wt. % of paper, 1–35 wt. % of gypsum, and 3–12% of water, and also states that clay, fuller's earth, and vermiculite are employed in cat litter compositions.
U.S. Pat. No. 4,638,763 issued Jan. 27, 1987 to Greenberg, teaches the addition of sodium sulfate to a litter box absorbent material to facilitate removal of solid absorbent material from the litter box, and teaches that clays such as montmorillonite and hectorite are suitable as absorbent material.
U.S. Pat. No. 4,685,420 issued Aug. 11, 1987 to Stuart, discloses an animal litter composition comprising a water-absorbing polymer such as a polyacrylate combined with a porous inert solid substrate such as clay.
U.S. Pat. No. 5,000,115 issued Mar. 19, 1991 to Hughes, discloses the use of a water-swellable bentonite clay as an absorbent litter material. The clay absorbs the liquids in animal waste which on contacting the clay agglomerates it into a stable mass easily separated from the unwetted and unsoiled portion of the composition.
Commonly assigned U.S. Pat. No. 5,295,456, issued Mar. 22, 1994, discloses a deodorizing agglomerated sodium bicarbonate additive which may be used in swellable bentonite clay litter compositions. The additive comprises sodium bicarbonate particles which are substantially coated with a mineral oil, and then blended with a powdered siliceous material, e.g., expanded perlite, having a bulk density significantly lower than the density of sodium bicarbonate. The oil-coated particles of bicarbonate are stably adhered to and agglomerated with the particles of the siliceous material.
Commonly assigned U.S. Pat. No. 5,303,676, issued Apr. 19, 1994 to Lawson, also discloses animal litter compositions containing a water-swellable clay and a deodorizing agglomerated sodium bicarbonate component.
The present assignee has marketed under the Arm & Hammer® brand an animal litter comprised of a “non-clumping” clay and a small amount of a compacted sodium bicarbonate. Traditional clay litter is of a larger particle size than the clumping or scoopable clays, and granular sodium bicarbonate segregated from the product. The use of the compacted bicarbonate improved the product homogeneity and reduced product segregation.